It's becoming more of a growing trend between married couples: the idea of living apart.

There are more than 3.5 million commuter marriages in the United States. According to the U.S. Census Bureau, that number has more than doubled since 1990.

About 1.7 million married couples who reported living apart said they are doing so for reasons other than legal separation. A recent study found nearly three in five couples who live apart said they do it because of work or financial reasons.

A 2009 UCLA study found those who are likely to live apart frequently live in urban areas, are better educated and tend to be younger. But that does not mean only younger couple are choosing to live apart. The AARP estimated the number of married couple 50 years and older who live apart tripled between 2001 and 2005.